Automatic hovering control system for submarines



T. E. ALLEN Feb. 28, 1961 AUTOMATIC HOVERING CONTROL SYSTEM FOR SUBMARINES Filed April 11, 1955 2 Sheets-Sheet 1 Feb. 28, 1961 Filed April l1, 1955 T. E. ALLEN AUTOMATIC HOVERING CONTROL SYSTEM FOR SUBMARINES 2 Sheets-Sheet 2 Lunar/0N Re veRS/BLE MorvR PUMP TTR-4 IN VEN TOR.

AUTOMATIC HOVERING CONTROL SYSTEM FOR SUBMAES Thomas E. Allen, Schenectady, NSY., assigner, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 11, 1955, Ser. N0. 500,707

Claims. (Cl. 114-16) This invention relates to automatic hovering control systems for submarines and more particularly, to an automatic hovering control system for a submarine for controlling intake and expulsion of sea Water ballast in a quiet and stable manner tto hold the submarine at a constant depth when the submarine is submerged and has no longitudinal component of motion through the water; the invention also is for use in making controlled changes in the depth of the submarine in the absence of a longitudinal component of motion through the water.

The term hovering as used in this description refers to submarines and describes a static situation where a submarine remains at a substantially constant depth in the absence of a longitudinal component of motion. For a submarine to remain at a constant depth, it is necessary that the sum of the vertical forces acting on the submarine be zero. When a submarine has no component of motion along its longitudinal axis, there are no hydrodynamic forces acting on the submarine. Thus, the bow and stern planes have no eifect upon holding depth. The submarine weight, otherwise known as overall trim and the buoyant force of the water are the only vertical forces present. The submarine moves vertically toward a depth corresponding to a balance between its Weight and the buoyant force of the water displaced by the submarine hull. 'When these forces are equal and opposite, the submarine remains at substantially a constant depth. This balance is delicate; in practice, it is almost impossible to attain this balance. Once an unbalance exists, the submarine will move up or down as the case may be. Furthermore, if no action is taken, the submarine either will surface or go to the bottom. This is a manifestation of the fact that when the pressure on the submarine changes the volume displaced by the submarine changes and therefore the displaced water weight changes. lf the submarine is slightly heavy, it will sink but as it sinks the hull compresses so that the buoyant force is smaller. The submarine therefore looks heavier and it sinks faster. This is a cumulative process. If the submarine is not resting on a layer of high density water or under a layer of low density water the submarine would surface or sink to the bottom if unattended.

To maintain a submarine at a fixed depth, i.e. to cause it to hover, it is necessary to adjust the weight of the submarine by controlled transfer of sea water into or out of a ballast tank or tanks until a neutral buoyancy is attained. A submarine tends to drift away from a given depth principally because it is out of trim. Sea currents in some cases may be important but in general they are not the chief cause of deviation.

lt is possible to cause a submarine to hover by manually controlling the trim pump which operates at about 200 gallons per minute. This tends to be noisy, requires skill, and at best results in a fairly large depth oscillation, on the order of ilO ft.

One hovering control system for submarines in pressent use includes a pressurized ballast tank or tanks. The ballast tank pressure is made equal to the sea water Y 2,972,972 Patented Feb. 2S, 196i pressure outside the hull of the submarine either lby bleeding air from a high-pressure storage bottle located inside the submarine into the ballast tank or by valving air out of the ballast tank into the hull of the submarine. By keeping the pressure in the ballast tank substantially equal to the sea water pressure around the submarine, it is possible to use a low-power, low-pressure ballast pump for transferring sea water ballast between the ballast tank and the sea. However, this system has several overriding disadvantages. The most prominent disadvantage is that the air valving is noisy. When a submarine is hovering to escape detection, the desired result is partially compromised by a noisy hovering system. Secondly, air noise is psychologically disagreeable thereby adversely affecting nervous stability of submarine personnel. Thirdly, the air released from the tank into the hull must be pumped back into the high-pressure storage bottle making it necessary for this system to have compressor equipment. Besides the usual disadvantages stemming from the use of additional power consuming equipment, compressor equipment has the additional disadvantage of contributing more noise. Finally, this system is relatively unstable in operation. The instability may be manifested by an oscillation either in tank pressure or submarine depth or both. This is due to the fact that controlling the pressure in a ballast tank so that it remains equal to the depth pressure While changing the volume of sea water ballast in the ballast tank is a tricky operation; in part, it is tricky because the pumping rate varies considerably with change in the difference of pressure between that in the ballast tank and sea pressure. Instability wastes power, causes increased generation of noise which increases chances of detection, and is further disagreeable because it is accompanied by poor control. When personne] cannot maintain positive control over the operation of their equipment, they lose confidence in the equipment. In a submarine, this can have a disastrous effect on morale.

The automatic hovering control system of this invention is adapted to store information on a desired depth hereinafter also referred to as order depth, the system operates in response to voltage signal information. The signal information is a function of the instantaneous combined inlluence of-three variables. One variable is the algebraic difference between order depth and actual depth. Actual depth is hereinafter also referred to as depth error. Another variable is the vertical component of submarine velocity hereinafter also referred to as depthrate. A third variable is the rate of change of deptherror plus depth rate. ln other words, the system operates as a function of the instantaneous combined influence o-f depth error, depth rate, and depth acceleration. Generally, this system includes a reversible pump for forcing sea water ballast into or out of ballast-retaining tanks in the submarine. These tanks may be conventional variable ballast tanks. In a preferred arrangement the submarine would include main fuel oil ltanks that are in fluid communication with the sea water outside the submarine hull and variable fuel oil tank(s) that are in iluid communication with the main fuel oil tanks. The reversible .pump is connected in series between the variable fuel oil tanks and the main fuel oil tanks. To take on sea water ballast, fuel oil is pumped from the ma-in fuel oil tanks into the variable fuel oil tanks thereby permitting sea water ballast to liow into the bottom(s) of the main fuel tanks. For expelling ballast, the procedure is reversed. This arrangement wherein the reversible pump pumps fuel oil is preferred because the reversible pump has a very short life when it is used to pump sea water at the high pressures encountered in service.

yThe control mechanism for the pump includes a compensated pressure-responsive device such as a Bourdon position. A spring is used for applying a variable reference force to or for displacing by a variable amount one partof the electrical proportional pickoi unit. When the force(s) applied to the parts of the electrical proportional pickoit unit are such that its parts are relatively disposed in null position, the pickoff generates no error voltage signal. This is the case when the ordered depth andactual depth are equal. voltage signal due to a difference between ordered depth and actual it is utilized for prompting the control circuit .to cause the reversible pump to operate for reducing the The error voltage signal fromA error voltage to zero. the electrical proportional pickol `is fed into a phase* sensitive amplifier. A follow-up motor co-nnected in circuit with the phase-sensitive amplitier rotates at a speed which varies with the power it obtains from the phasesensitive'amplitier; i.e. the amplitude of the error signal. Its direction corresponds to the phase of the error signal voltage. The follow-up motor is mechanically connected to a tachometer, to the rotor of a synchro or its equivalent for this purpose such as a potentiometer, and to the spring used for applying a variable reference force to the electrical proportional pickoi unit. The order depth is set by adjusting the stator of the synchro. The synchro produces the depth error signal its magnitude depending upon the angular deviation of its rotor from electrical zero position. The tachometer produces the depth rate signal. Part of the energy from the tachometer is fed 'back to the amplier for stabilizing circuit operation and to assure an accurate depth rate voltage signal. The depth error and depth rate signals are fed into a stabiliz ing network which adds a signal which is proportional to the rate of change of depth error plus depth rate. The resultant combined signal is fed into a power ampliier which controls the power output of an amplidyne. The power output of the amplidyne is fed into a motor coupled to the pump. A second tachometer is used for stabilizing system operation. The second tachomcter generates a signal voltage which is proportional to the speed of the pump. The pump runs at a speed determined by the combination of depth-error voltage, the depth rate voltage, and the rate of change of depth error and depth irate plus the voltage feedback from the tachometer. The

'use of pump rate feedback results in tight control of the pump speed even through the load on the pump motor varies with depth.

At every depth, the pump motor must develop the ltorque necessary to withstand the sea pressure. This torque is substantially constant at a given depth whether the pump is motionless or operating. This torque increases with depth. Furthermore, because of pump slip the pumping out flow for a particular pump speed decreases as the depth increases. For a given heavy out of trim, these ettects cause a larger departure from order depth at increasing depths. When the hydrostat signal calls for zero llow, the zero ow pump speed must be increased as the depth is increased. The hydrostat operates a potentiometer balance adjustment to accomplish this result. The potentiometer is connected in one of the amplifier biasing circuits.

An object of this invention is to provide `an automatic hovering control system for submarines.

A further object is to provide a stable automatic hovering control system Vfor submarines.

A further object is to provide automatic hovering control system for submarines which accurately hold actual depth in correspondence with order depth.

A further object is to provide a quiet-in-operation automatic hovering control system for submarines.

When there is an error.

A further object is to provide an automatic hovering control system for a submarine for use in moving the submarine to a specified depth when the submarine is not underway and to cause the submarine to remain at that depth.

A further object is to provide an automatic hovering control system for a submarine which is stable and quiet in operation and does not require air handling equipment.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a basic block diagram of a preferred embodiment of this invention, wherein solid lines indicate electrical connections and broken lines indicate mechanical connections,

Fig. 2 is a subcombination block diagram of the hydrostat servo block Yof Fig. 1, showing the relationship of mechanical and electrical elements,

Fig. 3 is a detailed showing of one form of proportional pickot adapted for use in the hydrostat servo of Fig. 2, and

Fig. 4 is a partial block diag-ram of a modification of the invention shown in Fig. 1 showing only the modified portion of the system.

This invention (Fig. l) includes a hydrostat servo 22 which produces a depth-error and a depth-rate signal voltage. An adjustable depth-order knob 24 in hydrostat servo 22 provides information to the system on the desired depth. The hydrostat servo 22 conventionally communicates with the sea Water outside of the hull of submarine 28 by means diagrammatically shown at 26 to get the information on actual depth. The difference between the actual depth of the submarine 28 and the dcsired depth is expressed by the hydrostat servo 22 as a depth-error output voltage. The hydrostat servo 22 further includes means for generating a depth-rate signal voltage. The output signal voltages of the hydrostat servo coupled into a stabilizing lead network 30; the action of the latter is in effect to add to the depth error plus depth rate signal another signal proportional to the rate of change off depth error plus depth rate. Expressed diterently, the iinal control signal has depth error, depthrate, and depth acceleration components; the depth error plus depth rate signal is transiently amplified for a short time. A power amplifier 32 is connected to stabilizing lead network 30. The amplifier 32 couples its output into the control field of amplidyne 34 whose armature is mechanically connected to and conventionally driven by drive motor 3S. The amplidyne 34 generates the power for driving D.C. pump motor 36. The drive motor 35 also is mechanically connected to and drives exciter 36a which supplies excitation current for the tield ofthe pump motor 36. The drive motor 35 is connected to an A.C. supply through a starter 37. The motor 36 is connected directly to reversible pump 38.

The pump 38 is selected for its ability to satisfactorily meet three operating conditions. The first condition is that the pump should have no slip. It should operate as a positive displacement pump. Slip is defined as leakage back through the pump when the pump is not running. The second condition is that the pump be as quiet as possible in operation. The third condition is that the pump have a relatively long useful life even though it operates at high pressures. The IMO pump is preferred as the best compromise. It is the pump lused on submarines for the hydraulic oil supply; it operates quietly and while it has some slip it is suitable for the purpose. The IMO pump is manufactured by the De Laval'Steam Turbine Company, Trenton, New Jersey. Essentially it is a screw type pump having a long single helical impeller actuating two idler' impellers.

Reversible pump 38 is in a iiuid circuit in series between variable fuel oil tanks 39 which are vented into the submarine and fuel-ballast tanks 40a and 4Gb at least one of which opens into the sea. Two or more variable fuel oil tanks 39 are located near the center of gravity of the submarine. Pump 38 pumps fuel oil. When the pump 38 pumps oil in a direction from the fuel-ballast tanks 40a and 40h into the variable fuel oil tanks 39 the submarine gets heavier moves downwardly since vsea water is drawn into the fuel-ballast tank 40b to fill the volume vacated by the fuel oil pumped into the variable fuel oil tank 39. Conversely when the pump 38 pumps oil in a direction from the variable fuel oil tanks 39 to the fuelballast tanks 40a and 40h, sea water is expelled from the fuel-ballast tank 4Gb making the submarine lighter and causing it to move upwardly. This arrangement for taking on sea water ballast and expelling sea water ballast by using fuel oil as the pumping medium permits the pump 3S to have a much longer effective life. if the p ump 38 were to pump sea water at high pressures it would suffer much more wear and thereby a much shorter life. When oil is pumped into the variable fuel oil tanks 39 and the sea water flows into the fuel-ballast tank 40b there is some change in fore and aft trim because of the difference in weight between the oil and the Water. This difference is slight and has very little effect on the overall trim. The fore and aft trim (pitch) is manually set and controlled by the diving officer of the submarine. The hovering control system has no effect on controlling the fore and aft trim.

A tachometer 40 is connected directly to the shaft of the reversible pump 38. The tachometer 40 generates an output voltage which is directly proportional to the speed of the pump 38. The voltage generated by tachometer 40 is combined with the control voltage signal input into the amplifier 32. The use of a tachometer feedback loop results in tight control of the pump speed.

The use of tachometer feedback around the pump motor is best explained by considering operation of the system with and without tachometer feedback. During design, a desirable value of pumping nate per foot depth error is selected. In a system without this tachometer, a low gain amplifier 32 would be used to control the motor. Assuming that the rated motor speed is 2000 r.p.m. and the pumping rate per foot depth error is such that feet of error gives 2000 r.p.m. then l foot of error should cause the motor to run at 100 r.p.m. A pump motor controlled in this manner only has a speed control range of about 20:1 `or lower. The lowest speed at which the motor will operate is 100 rpm. As the depth error increases from zero to one foot, the motor remains stationary until the one foot error is reached. Then the moto-r starts up and runs at 100 rpm. To hold the depth within one or two feet the system must start to pump long before there is a one foot error. When tachometer feedback is used, a high gain amplifier 32 can be used. Speed ranges of about 100:1 or better are then possible. This is an improvement of five times making it possible for the pump to start at 0.2 foot error. The error signal gradient and tachometer signal gradient establish the pumping rate per foot depth error ratio while without a tachometer feedback the error signal gradient and the amplifier gain establish the ratio; the same ratio is used in both cases.

Another advantage of the tachometer feedback around to pump motor is the decreased variation of the pump speed with load variations in depth. As depth increases the pressure head against which the pump operates increases. This decreases motor speed considerably if there is no tachometer feedback. With this feedback a slight decrease in speed increases the difference between the controlling signal and the tachometer feedback signal. The amplifier sees this increase and because of its high gain the increase in difference need only be small to cause the amplifier to supply the required additional torque to the moto-r.

The submarine is shown on the drawing as part of vt-he automatic hovering control system. This may 'seem odd because the lautomatic hovering control system is generally considered as extra equipment which is placed aboard the submarine to make it hover. Actually, however, the submarine is part of the complete hovering system.

When the submarine leaves the desired depth, the hydrostat servo 22 produces a depth error and depth rate signal which, when processed through stabilizing lead network 30 and amplifier 32 excites the control field of the amplidyne generator 34. The amplidyne 34 provides power to the pump motor 36 which in turn drives the pump 3S. The polarity of the signal input to amplifier 32 determines the direction of pumping while the magnitude of the signal determines the pumping rate. The pump pumps fuel oil whereby sea water is caused to move into or out of the submarines fuel-ballast tanks causing the submarine to rise or sink as is required. The tachometer feedback signal is added to the control signal input to the amplifier 32 and improves the operation of the system as explained above.

The hydrostat servo 22 (Fig. 2) comprises a first bellows 42 and a second bellows 44 each of which is fixed at one end to the submarine. The bellows 42 functions conventionally as a compensating member. The bellows 44 communicates in a conventional manner with the sea water outside the submarine. A compensated Bourdon tube yor an equivalent conventional pressure 4responsive device may be substituted for the bellows 42 and 44. The bellows 42 and 44 are mechanically connected at their movable ends to each other and are further connected to a pressure sensitive element 46 which is in the form of a lever arm pivoted at one end to the submarine at 48. The end of t-he pressure sensitive element 46 opposite the pivot 48 operates a proportional pickoff 50. A preferred form of the proportional pickoif 50 is shown in detail in Fig. 3. It includes an electromagnetic pickoff having a symmetrical E core S1 and a movable armature 52. The central leg of the core 5l is wound with an excitation coil and the other two legs support identical coils wound in opposition and connected in series. When the arm 46 is in its central or null position the latter coils produce no error voltage signal output because the voltages induced in the coils are equal and opposite. When the lever 46 is displaced from null position the latter two coils do produce .an error signal output because there is a net difference between the voltages induced'in the latter two coils; the magnitude of the difference or error voltage is a function of extent of angular displacement of the arm 46 from null position. The phase of the error signal generated depends upon the side to which the arm 46 is off null. Alternatively, the proportional pickoff may include a U-type core having a rotatable armature with the signal winding rotatable therewith as in a DArsonval movement. Other devices such as a low friction potentiometer also could be used as an equivalent of the electromagnetic pickoff shown in Fig. 3.

When the depth of the submarine changes, the bellows 44 is caused to expand or contract accordingly to move the arm 46 from its null position. The proportional pickoff 50 is connected in circuit with an amplifier 54. The error signal output from the proportional pickoff is fed into amplifier 54 which is preferably a phase sensitive magnetic amplifier. The output of the amplifier 54 is fed into a follow-up servo motor 56. The use o-f the servo motor makes it possible to obtain power amplification and a depth rate component as is explained below. The follow-up motor 56 is mechanically connected to a tachometer 58. The tachometer generates a D.C. signal voltage which is proportional to depth-rate. The servo motor is also connected to the rotor of a position signa-l device S2 having a rotor and a stator. The position signal device 62 preferably is a synchro or an equivalent device.. its stator is manually set to correspond to the order depth through the use of the depth-order knob 24. A mechanical depth-order indicator 68 is mechanically connected to the depth-order knob 24. A mechanical depth indicator 72 is ymechanically connected to the rotor of synchro 62. A gear train 60 is connected between follow-up motor servo 56 and the synhcro rotor. A nut 64 is connected to and rotates with the rotor of the synchro 62. The nut 64 threadedly engages for driving longitudinally a non rotatable screw 66. A pretensioned coil spring 68 designed for a linear relationship between stress and strain lis connected at one of its ends to the screw 66 and at the other of its ends to the arm 46. Assuming there were no screw 66, the spring would be pretensioned for one particular depth. In other Words if the ordered depth were 100 feet, the spring would be so pretensioned and secured at one end so that when the actual depth were 100 feet the moment applied by the bellows 42, 42 to the arm 46 and the moment applied by the pretensioned spring to the arm 46 would be equal and opposite when the piyoted arm 46 is in null position. Under these conditions if the actual depth changes, the moment applied to the pivoted arm 46 changes in direct proportion. The pivoted arm moves to a new position where the moments applied to the arm 46 by the bellows 42, 44 and the spring 68 are again equal and opposite. The angular deviation of the arm 46 from null position is directly proportional to difference between the moments applied to arm 46 by the bellows for the new position of the arm and for the null position. In other words the angular deviation is directly proportional to the difference between the ordered depth and actual depth. By adjusting the screw 66 longitudinally, the reference moment applied by spring 68 may be adjusted. Now assuming the hydrostat servo 22 is static. The ordered depth and actual depth correspond, the arm 46 is in null position and the rotor of synchro 62 is in electrical zero position. Because of out-of-trim let it be assumed that the submarines actual depth begins to increase. The moment applied by bellows 42, 44 to arm 46 increases and the arm 46 begins to move out of null position against the bias of spring 68. Instantaneously, an error signal is generated by the proportional pickoff 50. signal is fed into the phase sensitive magnetic amplifier S4 which provides power to the follow-up servo motor 56 which power is a function of the magnitude of the error signal. The follow-up motor drives the rotor of synchro 62 out of electrical zero position. The synchro produces a depth error signal proportional instantaneously to the angular deviation of its rotor from electrical zero position. The follow-up servo motor also drives the screw 64 in a direction for resisting the movement of arm 46 out of null position. lf the depth is changing fast the motor l56 rotates fast to oppose and stop the movement of the arm 46 away from null and then to bring it back to null as the change in depth approaches zero. The signal produced by the tachometer S is proportional to depth rate. A portion of the energy of the signal from tachometer 58 is fed into magnetic amplifier 'S4 opposing the error signal input. When the change in `depth stops and reverses so that the submarine goes back toward ordered depth the action of the hydrostat servo reverses to reduce the synchro error to Zero and restore the lnormal condition of the proportional pickolf 50.

A potentiometer 74 is connected to the rotor of synchro 62 and provides an output which is a function of depth. Because required motor torque and pump slip tends to increase with depth pressure, the potentiometer 74 is used to provide an output signal for a biasing circuit in the amplifier 32 for use in opposing this pump slip.

Fllhe tachometer 58 acts to stabilize the hydrostat loop. The pressure sensing elements are servoed through the use of the tachometer feedback in order to obtain a depth rate signal and also to drive several devices when the depth varies. Assuming the submarine is stabilized at the desired depth it is likely that a small depth oscillation on the order of plus and minus l foot of period of ten v minutes or longer may occur because of the unstable nature of the neutral buoyancy condition as Well as the very low lhydrodynamic damping at low velocities. The pump rate during this operation is low but continues `to The error` 1 in depth when not underway.

run atan average speed which increases with depth to prevent inboard iiow occurring when none is required.

In operation, the hovering control system operates to cause a submerged submarine to remain at a constant hovering depth when the submarine has no longitudinal motion through the Water. If the submarine is moving longitudinally, the diving oiiicer holds a depth by adjusting the trim and position of the planes. However, where the submarine has no longitudinal velocity, the planes become ineiective and the control of depth is accomplished solely by adjusting buoyancy or overall trim. This system serves to control the overall trim. Before it is put into operation the submarine is taken to the desired depth and leveled oi. The diving oicer generally adiusts the overall trim to within a specified maximum positive or negative buoyancy, and then directs that the engines be stopped and the hovering control system turned on. The hovering control system acts to control the overall trim to hold the submarine at the desired depth. It the submarine deviates from the desired depth the overall trim is automatically changed by the action of the automatic hovering control system to bring it back to the desired depth. The hovering control system can serve the additional purpose of making controlled changes It accomplishes this through a change in the setting of the depth-order knob. When this is done the hovering control system unbalances the overall trim to start the submarine moving toward the order depth. As the submarine approaches the new order depth, the control further changes the overall trim to slow up the rate of approach. When the submarine arrives at the new order depth, the hovering system operates to hold the submarine at this depth. Assuming that the automatic hovering control system is operating with perfect accuracy, then whenever the submarine is at the desired depth the depth-order indicator 68 and the depth-indicator 72 present the same readings, and the arm 46 is in null position whereby there is no error signal generated by the proportional pickoii 50. The follow-up servo motor 56 is stationary. Depending upon the submarine depth the pump 38 is operating for preventing inboard ilow in accordance with the potentiometer 74 setting. If the submarine begins to move toward a flower depth the sea Water pressure acting on the bellows 44 causes the arm 46 to rotate clockwise about the pivot 48 to a position dependent upon the summation of the moments acting upon it. When arm 46 moves out of null position the proportional picko 50 generates an error voltage signal whose magnitude is a function of the displacement of the arm 46 from null position at every instant. The error voltage signal from the pro-A portional pickoi 50 is coupled into an amplier S4. The latter furnishes power for causing the follow-up servo motor 56 to rotate at a speed which is a function of the magnitude of the error voltage signal from the proportional pickoi 50. The follow-up servo motor 56 drives the rotor of the synchro 62 moving it out of its electrical zero position relative to its stator. The rotor of the synchro is mechanically connected to the mechanical depth indicator 72 and also to the nut 64. The follow-up servo motor 56 rotates in a direction for causing the nut 64 to retract the screw 66 so as to apply more force to the arm 46 for moving it back toward null position. In eiect the pretensioning of the spring 68 is increased as would occur if the order depth were increased. The follow-up servo motor 56 also is mechanically connected to a tachometer 58. The synchro produces a depth error voltage signal and the tachometer 58 produces a depth rate voltage signal. The depth error voltage signal is an alternating voltage which is changed to a proportional direct current voltage signal by conventional means, not shown, and combined with the depth rate signal from the tachometer 58 for application to the stabilizing lead network 30.` A portion of the energy of the depth rate voltage signal from the tachometer 58 is utilized .to

oppose the error voltage signal from the proportional pickoff 50. This arrangement is used for stabilizing the Operation of the hydrostat servo and for obtaining more accurate depth rate information from the ta'chometer 50. The stabilizing network 30 processes the depth error and depth rate voltages for introducing a depth acceleration component into the resultant signal. 'Ihe resultant signal is applied to the power amplifier 32. The amplier 32 furnishes power to the control field of the amplidyne 34. The amplidyne 34 provides power to the pump motor 36 in conventional manner. The direction of rotation of pump motor 36 is such that it acts to force water out of the submarine fuel-ballast tank 40b for opposing the sinking movement of the submarine. The tachometer 4Q provides a pumping rate feedback voltage which opposes the signal input to amplifier 32 from the stabilizing network 30. The tachometer feedback loop permits the use of a high gain amplifier at 32 which results in better system accuracy. As sea water ballast is expelled from the submarine the downward acceleration of the submarine begins to decrease then stops. The submarine begins to decelerate, till its downward rate of movement is reduced to zero. The submarine then begins to accelerate upwardly back toward ordered depth. The force applied by the bellows 44 to the arm 46 begins to decrease causing the latter to start moving back toward null position. This reduces the signal output from the proportional pickoi 50 which is followed by a slowing down in the rate of rotation of the follow-up motor. The speed of the reversible pump 38 begins to decrease. When the arm 46 moves back to null position the follow-up servo motor 56 stops. However the synchro 62 still continues to generate a depth error voltage signal. The depth error voltage signal causes the pump 38 to continue to pump sea water out of the submarine. The arm 46 moves counterclockwise about pivot 48 causing the follow-up motor 46 to rotate in the reverse direction to bring the rotor of the synchro 62 back to electrical zero position. The polarity of the depth rate signal voltage from the tachometer 48 is of opposite polarity to what it was previously thereby acting to oppose the depth error signal. While this is happening nut 64 is rotated in the reverse direction to project the screw 66 so as to reduce the amount of pretension in spring 68 and the force applied to arm 46. The reversible pump 38 is driven in the reverse direction during a latter portion of the stabilizing activity of the system. The action finally stabilizes with the arm 46 back at null position and the rotor of the synchro 62 at electrical zero position. The pump slip balance potentiometer 74 which is directly connected to the rotor of the synchro 62 and is electrically connected between a power supply, not shown, and one of the biasing circuits of amplifier 32 is continuously adjusted in accordance with the actual depth of the submarine. When the submarine is at an increased depth where the sea pressure tends to cause sea water to flow into the fuelballast tank 40]; and causes fuel oil to flow past the reversible pump 38, the potentiometer 74 is automatically adjusted to a value for causing the amplifier 32 to supply' suliicient power to the pump motor 36 to oppose this pump slip effect.

When the automatic hovering control system is used for changing the submarines depth by a desired amount the action of the system is similar except that the depth error voltage signal from the synchro initiates the action instead of error voltage signal from the proportional pickofi 50 initiating the action. To change the depth, the depth-order knob 24 is rotated thereby rotating the stator of the synchro. The rotor of the synchro is no longer in electrical zero position relative to the stator. A depth-error voltage signal is generated by the synchro. The depth error voltage signal causes the pump to start operating. The system goes on to operate in a manner analogous to that explained above except that the pump works much longer to bring the submarine approximately to the ordered depth before the system lfunctions as above to cause the submarine to hover.

One practical embodiment of the described system which has been put into operation was designed to maintain depth within two feet between the limits of 60 and 200 feet, or within 5 feet at depths greater than 200 feet. The depth deviations may include any steady error as well as variable deviation. When a practical balance is achieved the variable deviation is very slow. lf the out of trim or initial velocity of the submarine is too great, the hovering control system is unable to control the depth of the submarine; when this happens it is necessary to control the ballast pumps manually in order to assist the hovering control system. In a class of submarine having a submerged mass expressed as a weight of 4,860,- 000 pounds, the particular embodiment referred to above handles a specified maximum out-of-trim of 1,00() pounds. The maximum pumping rate varies with depth but averages about 350 pounds per minute. The system may be turned on with any depth error. The extent to which the submarine is out of trim is the more critical transient. During actual tests starting with the system operating and holding a depth, depth changes up to 20() feet can be accomplished by the system by manually changing the order by depth setting the synchro stator. The overshoot of the selected depth may be a limiting condition in some cases.

A modification of the preferred embodiment of the invention `described above is shown in Fig. 4. Elements common to both modifications are not shown in Fig. 4. Generally, it differs from the preferred modification in the use of a hydraulic motor 82 of the scotch-yoke type or ball type instead of an electric-motor 36 as is shown in Fig. l. The hydraulic motor 82 drives a reversible pump 38 vas in Fig. 1. A two-stage hydraulic valve 84 is used for controlling application of the submarines hydraulic supply to the hydraulic motor 82 to control its speed and direction. The two-stage hydraulic valve is conventionally controlled by electromagnetic means energized from the amplifier 32. This modification is useful under certain conditions made evident by consid-eration of the following disadvantages and advantages of this modification over that of Fig. l. The main disadvantages of this modification are that it is an added drain on the submarines hydraulic supply where the submarines hydraulic supply generally has to satisfy large demands. The hydraulic motor 82 is noisy, e.g. 105 db as compared to about db for the pump motor 36 of the abovedescribed modification. However, its advantages are that it makes unnecessary several electrical machines of the modification of Fig. 1, namely, an amplidyne, an amplidyne drive motor7 a pump motor, and an excitor for the pump motor field, all of which are required for the modification of Fig. 1. These electrical machines are heavy, large, and noisy in operation. Though the substituted components are noisier, they are much lighter in weight and much smaller. Hydraulic systems are characterized by smoother operation at slow speed. Generally, this system would utilize the submarines hydraulic supply during the period that the supply is idle, i.e. during hovering. l

Obvioulsy many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A submarine automatic hovering control system comprising a submarine; tank means in said submarine vented into said submarine for containing a variable quantity of sea water ballast; a reversible pump; conduits connecting said tank means in fluid communication with said pump and the sea Water surrounding the submarine whereby the quantity of sea water ballast in said submarine is changeable by said pump; a' reversible motor connected to said pump for driving said pump; hydrostat servo means 'manually settable for storing information on a selected hovering depth for the submarine and communicating with the sea water surrounding the submarine for responding to the pressure of the sea water surrounding the submarine to continuously produce an error voltage signal output whose magnitude and phase are functions of the diiference betweenthe actual depth of the submarine and the selected hovering depth for the submarine and the rate at which its depth is changing; and means connected in circuit with and responsive to the hydrostat voltage signalfor energizing said motor for driving said pump in a direction for reducing lche hydrostat voltage signal output to zero.

2. An automatic hovering control system as described in claim 1 further comprising speed responsive means mechanically connected to said pump for generating a stabilizing voltage which is a function of pump speed; and means for conveying the stabilizing voltage to said motor energizing means in opposition to the signal voltage input thereto for stabilizing operation of said system.

3. The combination of a submarine and a hovering control system as described in claim 2 wherein said motor energizing means includes an amplifier for Vreceiving the signal from said hydrostat servo means, an amplidyne generator having a field winding connected to said amplier and providing outputI power to said pump motor.

4. In combination, a submarine having at least one tank in communication with the outside of the hull of said submarine `for containing a variable quantity of sea water ballast; a hovering control system for automatically controlling the quantity of sea water ballast in said tank whereby said submarine is caused to hover at a preselected depth, said system comprising a reversible pump, conduits for connecting said pump in fluid communication with said tank for controlling the quantity of sea water ballast in said tank; power means for causing said pump to force movement of sea water to or from said tank, said power means including an amplier, an amplidyne generator having a ield winding connected to said amplifier and a motor coupled to said pump and powered from said amplidyne generator; a manually settable hydrostat servo means connected in circuit with said power means and adapted to store information on a selected depth for the submarine, said hydrostat servo means including a compensated bellows in fluid communication with the sea water about said submarine, a pivoted arm connected to said compensated bellows, an electrical proportional pickoif operatively connected with said pivoted arm, a spring connected at one end to said pivoted arm, a screw secured to the other end of said spring, a nut threadedly engaged with said screw, a synchro, said nut connected to the rotor of said synchro, a depth order knob secured to the stator of said synchro, a mechanical depth order indicator secured to the stator of said synchro, a mechanical depth indicator secured to the rotor of said synchro, a follow-up,y servo motor, a reduction gear train connected between` the rotor of said follow-up motor and the rotor of said synchro, a rst tachometer connected to the shaft of said follow-up motor, a phase sensitive magnetic amplitier connected at its output end to said followup motor, means for conveying error voltage signal from said proportional pickup and a portion of the energy generated by said first tachometer to the input of said phase-sensitive amplifier so that energy from said first tachometer opposes the error voltage signal for stabilizing said hydrostat servo, whereby the output of said hydrostat servo includes a depth error voltage signal from said synchro and a depth -rate voltage signa-l from said rst tachometer; uid conduit means connected between said hydrostat servo means and the sea Water surrounding said submarine whereby said hydrostat servo means obtains information as to the actual depth of the submarine; a second tachometer connected to said pump for generating a stabilizing signal proportional to the speed of the pump; means for feeding the stabilizing signal from said second tachometer to said power means in opposition to the depth error signal.

5. The combination of a submarine and a hovering control system as described in claim l further including a stabilizing lead network between said hydrostat servo means and said motor energizing means for adding to the signal input to the latter a signal component which is a function of the rate of change of depth error plus depth rate.

l References Cited in the le of this patent UNITED STATES PATENTS 2,263,553 Borracci Nov. 25, 1941 2,555,357 Maspero June 5, 1951 2,579,220 Vine Dec. 18, 1951 2,704,936 v Vine et al. Mar. 29, 1955 

